[sara moradi]

Hi all,

Do you know how can I write a UDF for a new material with new chemical formula?

[pakk]

Maybe. It depends on what you want the UDF to do... You forgot to say that.

[sara moradi]

Originally Posted by pakk

Maybe. It depends on what you want the UDF to do... You forgot to say that.

I want to calculate molecular weight (molwt) of species.

[pakk]

Originally Posted by sara moradi

I want to calculate molecular weight (molwt) of species.

And why do you want to use a UDF for that? Why don't you just add a material and change the molecular weight?

[sara moradi]

Originally Posted by pakk

And why do you want to use a UDF for that? Why don't you just add a material and change the molecular weight?

because my type of material is droplet-particle, and there is no icon for molecular weight!

[pakk]

Originally Posted by sara moradi

because my type of material is droplet-particle, and there is no icon for molecular weight!

Maybe you should rephrase your question to what you really want.
On the first post you forgot to say what the UDF should do, and on the second post you forgot to say that you have a droplet-particle. I'm afraid to start to answer, because maybe you forgot to mention something else...

Why do you need molecular weight for a droplet? For which physics is that relevant? What should the weight be? A constant that you know? Calculated from other values? Don't make us guess what you need, tell us?

[sara moradi]

Originally Posted by pakk

Maybe you should rephrase your question to what you really want.
On the first post you forgot to say what the UDF should do, and on the second post you forgot to say that you have a droplet-particle. I'm afraid to start to answer, because maybe you forgot to mention something else...

Why do you need molecular weight for a droplet? For which physics is that relevant? What should the weight be? A constant that you know? Calculated from other values? Don't make us guess what you need, tell us?

there is no different whether the molecular weight is constant or not. i'm simulating the heat and mass transfer in multi components. but i don't have access to change the molecular weight of my material (droplet- particle), so i guessed to change its chemical formula instead of changing the molecular weight (as i mentioned in the first post). however, changing the molwt would be an easier strategy.
thanks for your time and consideration Pakk.

[pakk]

If the molwt is not given in the Fluent screen, it is because it is not used in any calculation at all.

You seem to have a model in your mind where heat transfer depends on molecular weight. Which is fine, but apparently Fluent does not use such a model.

So I guess that your real question is: how can I use a model that includes the molecular weight in the heat transfer calculation of your droplet-particles?

Honestly: I don't know. Sorry that I could not get the answer, but I hope I helped to clarify your question.

[sara moradi]

Originally Posted by pakk

If the molwt is not given in the Fluent screen, it is because it is not used in any calculation at all.

You seem to have a model in your mind where heat transfer depends on molecular weight. Which is fine, but apparently Fluent does not use such a model.

So I guess that your real question is: how can I use a model that includes the molecular weight in the heat transfer calculation of your droplet-particles?

Honestly: I don't know. Sorry that I could not get the answer, but I hope I helped to clarify your question.

No! there is a model of heat and mass transfer which is associated with the molecular weight. why you change my question in every post! you can check the DPM-heat and mass transfer in the fluent manual.

[pakk]

If the model uses molwt, Fluent needs to know this number, so there has to be an input field for this.
So there are three options:
1. There is an input field for molwt for particle droplets, but you can not find it, possibly because you are looking in the wrong place.
2. The heat transfer model that uses molwt can not be used for droplet particles.
3. The programmers of Fluent made a very stupid mistake.

I don't know which of the three is the truth, but in no case is the solution "write a UDF for molwt".
Note: I am only changing your question to help you. You are asking the wrong problem. It's an X/Y problem, if you know what that means.

[sara moradi]

Originally Posted by pakk

If the model uses molwt, Fluent needs to know this number, so there has to be an input field for this.
So there are three options:
1. There is an input field for molwt for particle droplets, but you can not find it, possibly because you are looking in the wrong place.
2. The heat transfer model that uses molwt can not be used for droplet particles.
3. The programmers of Fluent made a very stupid mistake.

I don't know which of the three is the truth, but in no case is the solution "write a UDF for molwt".
Note: I am only changing your question to help you. You are asking the wrong problem. It's an X/Y problem, if you know what that means.

thank you Pakk for your response.

I realized that in the Create/edit material dialog box there is a button named "user-defined database" in which you can define your material with a specific chemical formula as well as any properties. I share it since it would be useful for others.